GABA is a functionally important, inhibitory neurotransmitter in the rabbit retina. Since many of the components of the GABA transmission system develop postnatally in the rabbit retina, this system offers an excellent opportunity to examine the precise developmental pattern of this prominent transmitter system and to investigate the mechanisms which might be important in the control of some developmental processes. We will examine the precise anatomical distributions of GABAERGIC AND GABAreceptive cells during postnatal development by light and EM autoradiography. Biochemical analyses of GABA uptake, release and receptor binding during postnatal development will be used to quantify the developmental changes observed autoradiographically and to establish the pharmacological sensitivity of components of the GABA system to a variety of specific pharmacological agents. Assessment of the functional maturation of the GAB output will be made by monitoring the effect of GABA on two cells known to receive GABA input, i.e., cholinergic and dopaminergic amacrine cells. Maturation of synaptic inputs to the GABA neurons will be assessed by monitoring the sensitivity of the GABA system to various other neurotransmitter receptor agonists and antagonists. Our preliminary experiments have demonstrated a precocious induction of GAB receptors after inhibition of GAB uptake on day 1 after birth. Future experiments will focus on the mechanism of receptor induction and will include the investigation of other possible interactions between components of the GABA system during development. These data will contribute significantly to our understanding of the types of cells which use GABA as a transmitter; their distribution, synaptic inputs and outputs; and the mechanisms by which pre andpostynaptic components interact during postnatal maturation of the GABA system.